Heat exchangers are used in various capacities in automotive applications. For example, all automobiles having water cooled engines employ a radiator and a heater core. Automobiles equipped with air conditioning also include an evaporator and a condenser. These heat exchangers are made from aluminum and consist of two spaced header tanks interconnected by flow tubes having cooling fins extending therefrom. Fluid is circulated through the header tanks and flow tubes to effect the necessary temperature drop.
The header tanks and flow tubes and cooling fins are rigidly attached to one another by brazing. It has been found that this brazing operation can be most efficiently accomplished in an oven for mass production applications. The prior art teaches the use of radiant braze ovens whereby the heat exchangers are fed through a heated muffle tube with radiant heat energy being used to raise the temperature of the heat exchangers to the braze liquification temperature.
The prior art has found that by using the principles of convection heat transfer, the heat exchanger workparts can be more efficiently and quickly raised to the braze liquification temperature. Examples of these prior art convection braze furnaces may be found in U.S. Pat. No. 3,756,489 to Chartet, issued Sep. 4, 1973, U.S. Pat. No. 3,882,596 to Kendziora et al, issued May 13, 1975, and U.S. Pat. No. 4,501,387 to Hoyer, issued Feb. 26, 1985. The Chartet and Kendziora et al references disclose sectioning the braze furnace into zones, with the final zone comprising a cooling zone for solidifying the braze material prior to the workparts exiting the braze furnace. However, these prior art braze furnaces are deficient in that the rate of heat energy absorbed from the workparts in the final cooling zone could not be accurately controlled. If the workparts are cooled too quickly, warpage will occur. Conversely, if the workparts are not cooled quickly enough, the workparts will exit the braze furnace with the braze material in a partially congealed state bonding to the atmosphere curtain in the exit vestibule. Hence, precise control over the rate of workpart cooling in the prior art is not available.